Saw chains wear down as they are used, and they must be ground to restore their cutting edge. The grinding of a saw chain generally involves grinding one blade at a time with a tool such as a rat-tail file with the saw chain being mounted to the chainsaw. However, this is done manually, and good grinding requires considerable skill. Also, it would occur that as grinding proceeds, the shape of the various blades becomes uneven, so that eventually the chain becomes so unbalanced and it cannot cut any longer.
In one grinder proposed in view of the above facts, a file is attached to an electric tool and fixed relatively with respect to the saw chain, so that the grinding is performed thereby mechanically. In one of this type of grinder, the saw chain is removed from the chainsaw main unit (hereinafter called “main unit”), set on a grinding stand or the like, and then grinding is performed in this state; and in another type, the saw chain is ground while being mounted on the main unit. The former type affords a more accurate grind; however, it entails extra work of removing and reattaching the chain, and the grinding cannot be performed on-site. The latter, on the other hand, is more convenient; however, it takes time to attach the grinder, and set-up can be difficult.
Japanese Patent Application Laid-Open No. 2005-288676 discloses the latter type of grinder, and it describes that the grinder can be set up merely by inserting a guide body equipped with an electric motor from above the saw chain. However, since the spacing between the ribs and pressing plates that sandwich the guide bar of the saw chain from the left and right is set so that extra space is assured with respect to the thickness of the guide bar, the pressing plate must be pushed in the direction of grinding while being kept upright by being constantly pressed against the guide bar, which makes operation difficult. The grindstone used in this prior art example is a cylindrical grindstone, and such a grindstone wears down quickly; and since the working radius is small, the grinding capability is inferior. Furthermore, in this prior art example, the cylindrical grindstone is rotated at high speed; however, if the grinding speed is too high, grinding heat may make it impossible to keep the blade face at the optimal hardness. In contrast to this example, the grinder disclosed in Japanese Patent Application Laid-Open No. H10-128619 makes use of a disk-shape grindstone. However, since the grinder is supported by support legs, etc., the apparatus becomes bulkier. In addition, in this example, since the setting of the grindstone into the proper position is accomplished by turning a knob provided on the support legs, high skill is required, and also it takes more time.